Unref'd timeouts should not be reported as open handles #8939
Description
🐛 Bug Report
Timeout.unref() in node tells node not to let the timeout block process shutdown. That means that these timeouts are never going to stop Jest from shutting down, but --detectOpenHandles still reports them as such.
Any intervals or timeouts that has been unref'd should not be reported by Jest as an open handle.
I'm not actually a Jest user myself - I'm reporting this as I received a bug report on a testing library I maintain, because Jest is complaining about an unref'd interval used here.
To Reproduce
In any test, include an unref'd timer:
const interval = setInterval(() => {}, 10000);
interval.unref();This test will exit happily with no problems.
Run this test without the unref() line though and it won't, and you'll see a Jest did not exit one second after the test run has completed warning.
However, if you run this test with --detectOpenHandles then regardless of unref(), this setInterval will always be reported as an open handle.
Expected behavior
--detectOpenHandles should not show a warning for this interval, but it does.
Suggestion
Since Node v11, there's a Timeout.hasRef() function, which can be used to check whether any timeout will keep the event loop active, or whether it's unref'd and will allow shutdown.
I'd be happy to put together a quick PR to fix this, if it's likely to be accepted? I think this is pretty easy to solve for node 11+: just filter the active timeout handles by the result of hasRef(), if present.
You could polyfill hasRef() for pre-v11 versions, but v12 is going to be the active LTS release in a month anyway, and this isn't a blocking issue, so I probably wouldn't bother.
How does that sound?